Expression of receptor activator of nuclear factor-kappaB ligand in synovial tissue: comparison with degradation of articular cartilage in temporomandibular joint disorders.

OBJECTIVE: The present study was performed to investigate the correlations between expression of the receptor activator of nuclear factor-kappaB ligand (RANKL) in synovial tissue and the degrees of synovitis, degeneration of articular cartilage, and adhesions in patients with internal derangement (ID) of the temporomandibular joint (TMJ). STUDY DESIGN: Expression of RANKL, detected immunohistochemically, and the severity of arthroscopic features (synovitis, degenerative changes of articular eminence, and adhesion) in 30 patients with ID of the TMJ were assessed and the correlations between them were analyzed statistically. RESULTS: RANKL expression was detected in the cytoplasm of synovial lining cells, endothelial cells, and fibroblast cells. However, there were no correlations between RANKL expression in any cell type and the severity of arthroscopic features. CONCLUSION: These observations indicated that the cellular source of osteoclastic differentiation exists in TMJ with ID and may provide insight into the mechanism of osteoclast differentiation.

Influence of surface roughness on crack formation in a glass-ceramic bonded to a resin composite base.

The objective of the present study was to assess the influence of the roughness of a loaded surface on crack formation in a mica-based glass-ceramic bonded to a resin composite base. Five different surface roughnesses were created on glass-ceramic discs by serial wet-grinding with silicone carbide abrasives. The thicknesses of the ceramic discs were 1.50 +/- 0.01 mm. Resin composite discs were bonded to the ceramic surfaces opposite to the ground surfaces using an adhesive resin composite cement and a silane coupling agent. A compressive load was then applied at the center of the ground ceramic surface. The loads at initial radial and cone crack formations in the ceramic were measured macroscopically. In three of the five groups, the initial radial crack formations could not be observed due to the high roughness of these surfaces. Statistical analysis was performed using Student's t test for initial radial cracks and one-way ANOVA for the cone cracks. There were no significant differences between the two groups for the initial radial cracks or among the five groups for the cone cracks (P < 0.05). The roughness of the loaded surface had no influence on crack formation in the bonded mica-based glass-ceramic.

Marginal toughness of bonded dental ceramics evaluated by determination of the crack length.

OBJECTIVES: The objective of this study was to evaluate the toughness of dental ceramics near a bonded interface using indentation microfracture. METHODS: The ceramics used in the present study were two leucite-reinforced ceramics (IPS Empress and Finesse), one lithia-based ceramic (IPS Empress 2) and one mica-based ceramic (OCC). The ceramic discs were processed according to the manufacturers instructions and were bonded to resinous discs using a resin composite cement. The bonded specimens were sectioned perpendicularly, and micro-Vickers indentations were imprinted at several distances from the bonded interface in the polished ceramic sections. The lengths between the two ends of the radial cracks along the bonded interface were measured. RESULTS: Crack lengthening was recognized when the distance was within 70 microm. In each ceramic, the indentation crack length at 40 microm from the interface was significantly longer than the length at the inner point of the ceramic material (p<0.05). The order of the mean indentation crack lengths at 40 microm was OCC>Finesse>IPS Empress 2>IPS Empress, while the order at 490 microm was Finesse>OCC>IPS Empress>IPS Empress 2. There was a difference between the orders at 40 microm and at 490 microm. SIGNIFICANCE: The behaviour of the indentation crack near the interface differs from that which is distant from the interface. Therefore, it is impossible to estimate the marginal toughness of the ceramic based on the indentation microfracture at the inner point of the ceramic.